This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
佂 combines the person radical 亻 with 正, but the exact historical development and original meaning are uncertain.
A person 亻 standing beside 正 (correct, upright) might suggest a person who is upright or proper, but the actual meaning is unclear.
For セイ, imagine a person 亻 standing straight and correct 正, like a saint: saint -> セイ.